Various broadband microwave attenuators are known to the art which contain a single resistive surface which forms both the series attenuated path between the primary conductors and a shunt impedance path between the primary conductors and the ground conductor. The resistive element of such devices is ordinarily deposited on a rectangular plane surface of a ceramic member.
One of the difficulties encountered in the manufacture of these devices is the problem of accurately calibrating attenuators having high db values; (e.g. 40 db or above). To combat this difficulty, recent prior attenuators have two or more separate resistive elements deposited on the same ceramic member which are series connected by a conductor. In this manner, the calibration problem associated with large db attenuators is averted by constructing what is essentially two or more smaller attenuators (the sum of whose db values equals the desired db value) on the same ceramic member and connecting the "sub-attenuators" in series.
Another difficulty encountered with attenuators is an inherent tendency to provide less attenuation at high frequencies. In other words, the db value of the attenuation tends to decline as the frequency of the applied signal increases.
The present invention provides a microwave attenuator having two or more resistive elements disposed on a single ceramic member as described above, with an inductive element connected in series between the two resistive elements to compensate for the tendency of the db value of the attenuator to decline. Since the effect of an inductance increases with frequency, the inductive element effectively compensates for the inherent drop in the db level of the attenuator element with increasing frequency. Thus, the overall db level of the attenuator is maintained at or substantially near its rated value over a wider range of frequencies.
As will subsequently be described in greater detail, the inductance in the attenuator element is created by bridging a narrow gap in the center conductor which provides the electrical series connection between the two resistive elements with a conductive element of substantially reduced width relative to the center conductor between the two resistive elements. As is well known in the microwave art, the substantial change in the width of the center conductor generates an inductance, the value of which is dependent upon its length and its width. By varying these dimensions, a suitable inductance can be created which will properly "correlate" with the inherent decline in db value of the attenuator to offset same.
In view of the above explanation, it will be appreciated that a microwave attenuator is provided which includes an inductive element which effectively compensates for the inherent drop in the db level of the attenuator element which occurs at high frequencies, thereby increasing the effective operating bandwidth of the attenuator.